In current large-scale networks, information flows through a series of nodes or network elements in the network from one location or site to another. As the network grows, more and more transmission lines may be added to handle the heavy traffic flow between network elements. Network switches are used to connect one transmission line to another and to manage information flow through a network. As networks increase in size and complexity, more switches and transmission lines are added. An example of such a network switch is the MultiWave CoreDirector switch, manufactured and distributed by CIENA Corporation of Linthicum, Md.
To enhance reliability of communications through networks, various line/path protection schemes can be used, as is known in the art. For example, Sub-Network Connection Protection (SNCP) is a standard protocol in Synchronous Optical Network (SONET)/Synchronous Digital Hierarchy (SDH) systems (reference to SONET hereinafter shall mean either SONET or SDH). The protection protocol can include a working line and a protect line. Typically, the working line and protect line are matched in capabilities (e.g., number of channels, bandwidth, and the like). In the event of a failure on the working line, the protect line can be used to maintain the network connection and reduce down time. Service providers often commit to various class of service requirements that can specify penalties for network down time. Therefore, service providers can lose significant revenue due to communication line failures. Accordingly, many service providers use protected lines to reduce down time on critical services.
Various protection techniques are known in the art, such as ring-based, linear and mesh protection. An advantage of a ring-based network protection scheme is that the traffic between two nodes on the ring can be re-routed over a predetermined secondary route, if a failure should occur in a primary route. An example of such a network is a SONET ring, with predefined primary and secondary, or working and protection, routes between the nodes on the ring. The routes may be over redundant rings, which pass traffic simultaneously in opposite directions. Such a system is commonly referred to as a “unidirectional ring.”
When a failure or a significant degradation in, for example, the primary path, is detected on a SONET ring, the system must automatically re-route, or switch, affected traffic from the primary path to the secondary path. The re-routing, which is commonly referred to as “protection switching,” is performed in unidirectional systems by the destination nodes, that is, by the nodes that terminate the traffic or route the traffic off of the ring to a user or another network. In the example, the destination nodes switch from receiving the affected traffic over the primary path to receiving the traffic over the secondary path.
For example, in a 1:1 protection scheme two redundant paths are provisioned, but only one path is used. In contrast a 1+1 protection scheme, allows both paths (e.g., the working and the protect) to concurrently transmit packets. Other schemes include, multiple working paths sharing a protect path (referred to as 1:N protection). Protection topologies also vary depending on the network topology and can be implemented in linear, ring, mesh configurations or Virtual Line Switched Ring (VLSR). A Virtual Line Switched Rings is described in more detail in U.S. Pat. No. 6,654,341, Virtual Line Switched Ring, filed on Oct. 19, 1999, which is herein incorporated by reference in its entirety. Further, protection mechanisms can be implemented at the link level such as automatic protection switching (APS) or at higher levels such as ring level bi-directional line switched ring (BLSR).
FIG. 1 illustrates a ring topology 100 having a working path 150 and a protect path 160 interconnecting nodes 110, 120, 130 and 140. For example, using a 1:1 protection scheme working path 150 can be used to transmit information between nodes 110–140. Protect path 160 is provisioned, but the information is not transmitted over the protect path 160. However, in the event of a failure in a portion of path 150, protection switching will cause the information transmission to be switched to protect path 160.